Name that timing chain game.... Where's Russ

[gotta240]

Motor- ka24de from 93 auto w/ 130k miles.
How can you tell when the timing chain has or needs to be replaced? (by looking at it, since i don't know the history of this motor)

The motor in question has a timing chain that says "O6E" on the two connecting links. I have another spare motor that says "japan" on the same links. I'm assuming that the factory nissan links say "japan" and that the one on my motor has already been replaced.

However, these are only assumptions and i figure only one or two people on here will actually KNOW for sure...Russ being one of them.

thanks in advance to anyone who KNOWS.